The present invention relates generally to methods and apparatus for submersible pumping systems. More particularly, the present invention relates to methods and apparatus for submersible pumps used in artificial lift systems for producing low flow rate oil, gas and coal bed methane wells.
Hydrocarbons, and other fluids, are often contained within subterranean formations at elevated pressures. Wells drilled into these formations allow the elevated pressure within the formation to force the fluids to the surface. However, in low pressure formations, or when the formation pressure has diminished, the formation pressure may be insufficient to force the fluids to the surface. In these cases, a pump can be installed to provide the required pressure to produce the fluids.
The volume of well fluids produced from a low pressure well is often limited, thus limiting the potential income generated by the well. For wells that require pumping systems, the installation and operating costs of these systems often determine whether a pumping system is installed to enable production or the well is abandoned. Among the more significant costs associated with pumping systems are the costs for installing, maintaining, and powering the system. Reducing these costs may allow more wells to be produced economically and increase the efficiency of wells already having pumping systems.
The operation of a downhole pumping system depends on providing energy to the submerged pump components that generate hydraulic power that lifts fluid from the well. Thus, the transmission of energy between the surface and a downhole pump is one the key elements that determines the efficiency, size, and operating characteristics of a downhole pumping system. This energy can, for example, be in the form of mechanical energy, hydraulic energy, or electrical energy. For example, a rod pump uses a reciprocating steel rod as the means to transmit mechanical energy from the surface to the downhole pump. Rod pumps may be subject to serious limitations, especially under harsh conditions that tend to cause wear in the pump due to the interaction of the pumped fluid with the pressure generating (piston-cylinder) portions of the pump. Other types of pumps rely on electrical power to drive a submerged pumping unit but the use of electric systems is often limited by size restrictions or infrastructure limitations.
There remains a need to develop lower cost, more efficient methods and apparatus for pumping fluids from a low pressure wellbore that overcome some of the foregoing difficulties while providing more advantageous overall results.